There are many different types of packaged nutritional liquids suitable for oral administration to humans, which compositions typically comprise various combinations of macro and micro nutrients. Many of these packaged liquids are formulated as milk or protein-based emulsions for use as sole or supplemental sources of nutrition. These packaged emulsions are often manufactured as oil-in-water emulsions comprising fat, protein, carbohydrate, vitamins, and minerals, some examples of which include ENSURE® Nutritional Liquid and GLUCERNA® Shakes available from Abbott Laboratories, Columbus, Ohio USA.
During the manufacturing process, these packaged nutritional compositions are sterilized to reduce microbial contaminants to the extent necessary to render the compositions suitable for oral administration to humans. These processes often include thermal processes such as retort sterilization and aseptic process sterilization. A typical retort process involves introducing the nutritional composition into a suitable container, sealing the container, and then heating the sealed container and its contents for a time period and at temperature sufficient for sterilization. An aseptic sterilization process on the other hand typically involves separately sterilizing the interior of a food grade container and a nutritional composition and then combining the sterilized container and the sterilized nutritional composition in a clean room environment and sealing the container.
Aseptic sterilization processes for sterilizing nutritional compositions have grown in popularity over the years. By using such processes, nutritional products do not have to be heated to a temperature as high as that required for retort sterilization. These lower temperatures are generally preferred as they result in a decreased amount of product oxidation as compared to higher temperatures. Additionally, aseptic sterilization of plastic containers is generally preferred over retort sterilization of plastic containers as retort sterilization requires high temperature heating of the plastic container which can result in failure of the plastic container during sterilization.
Although aseptic sterilization has grown in popularity and has several advantages over retort sterilization, aseptic sterilization does require that the interior of the container be sterilized prior to the introduction of the sterilized nutritional composition. This interior sterilization is often performed by introducing a peroxide-containing solution, such as a hydrogen peroxide solution, typically in atomized form, into at least the interior of the container and drying the solution to produce a sterilized surface. Irrespective of the drying process employed, peroxide residue remains on the interior surface of the container. This residue can be problematic in some applications as it can, over time, migrate into the nutritional composition and cause a reduction in pH of the nutritional composition subsequently introduced into the peroxide-treated container.
The reduction in pH of the nutritional liquid over time due to oxidation can have numerous detrimental effects on the nutritional liquid inside the package including: (1) increasing the release of bound minerals, which in ionic form can compromise stability of the nutritional liquid due to precipitation; (2) increasing the amount of catalytic oxidation, particularly of iron and copper species; (3) increasing the amount of protein precipitation; and (4) increasing vitamin C destabilization. Any one of these unwanted effects can significantly reduce the commercial acceptability of the nutritional liquid.
There is therefore a need for stable nutritional compositions, such as stable protein or milk-based liquids or emulsions, that can be introduced into peroxide-treated aseptically sterilized containers and that are stable and resistant to a reduction in pH over time.